1. Field of the Invention
The present invention generally relates to semiconductor processing. Specifically, the present invention relates to semiconductor processing equipment and a turbo-molecular vacuum pump with increased pumping capacity for evacuating a vacuum processing chamber.
2. Background of the Related Art
Substrates are typically processed through various etch, chemical vapor deposition (CVD), physical vapor deposition (PVD), ion implanting and cleaning steps to construct integrated circuits or other structures thereon. These steps are usually performed in an environmentally isolated and vacuum sealed substrate processing chamber. The substrate processing chamber generally comprises an enclosure having a side wall, a bottom and a lid. A substrate support member is disposed within the chamber to secure a substrate in place during processing by electrical or mechanical means such as an electrostatic chuck or a vacuum chuck. A slit valve is disposed on a chamber side wall to allow the transfer of the substrate into and out of the substrate processing chamber. In CVD processes, various process gases enter into the substrate processing chamber through a gas inlet, such as a shower-head type gas inlet, disposed through the lid of the processing chamber. In PVD processes, various process gases enter into the substrate processing chamber through a gas inlet in the processing chamber. In each type of process, the gases are exhausted from the substrate processing chamber through the use of a vacuum pump, such as a turbomolecular pump, which is attached to a gas outlet of the substrate processing chamber.
Turbo molecular pumps are used in high (10xe2x88x927 Torr) or ultra-high (10xe2x88x9210 Torr) vacuum systems, exhausting to a backing pump that establishes a first pressure in the chamber. The turbo molecular pumps include a rotor with rows of oblique radial blades turning between a stator having inwardly facing rows of blades. The outer tips of the rotor blades approach molecular speed of the gas being pumped and when a molecule strikes the rotor, a significant component of momentum is transferred to the molecule in the direction of rotation. This transferred momentum causes the molecule of gas to move from the inlet side of the pump towards the exhaust side of the pump. Turbo molecular pumps are characterized by a rotational speed of 20,000 to 90,000 rpm and a pumping speed or capacity of 50 liters/sec. to 5,000 liters/sec.
FIG. 1 is a cross-sectional view of a typical turbo-molecular pump 10. The turbo-molecular pump 10 generally comprises a cylindrical casing 72, a base 74 closing the bottom of the casing 72, a rotor 40 disposed coaxially in the casing 72, a motor 20 coaxially disposed with the rotor 40, and a stator 30 extending radially inwardly from the casing 72. The casing 72 provides a support structure for the turbo-molecular pump 10 and includes an inlet port 12 disposed through the top of the casing 72. An outlet port 14 is disposed through the base 74 and is attached to a backing pump and an abatement system (not shown) for recovery or disposal of the gases. The motor 20 is an electrical motor that rotates the rotor 40 about an axis. The rotor 40 may be suspended by mechanical bearings 37 or by magnetic bearings in a floating condition with the casing.
Rotor blades 46 and stator blades 36 are shaped to pump gas from the inlet port 12 to the outlet port 14 and to prevent gas flow back into the vacuum processing chamber (not shown). The rotor 40 includes rows of rotor blades 46 extending radially outwardly in levels from a central cylindrical portion of the rotor that receives a portion of the motor 20. The stator 30, likewise includes rows of blades 36 extending radially inwardly in levels from the casing 72. The rows of stator blades 36 are arranged at alternating axial levels with the rows of rotor blades 46, and a plurality of spacer rings 38 separate different levels of stator blades 36 to ensure that the rotor blades 46 can rotate freely between stator blades 36. A xe2x80x9cfirst stagexe2x80x9d of the pump is defined by the first row of rotor blades 46 and the first row of stator blades 36 at the intake end of the pump. Each row of rotor blades 46 and corresponding row of stator blades 36 thereafter make up another stage and there are typically between 5 and 13 stages in a turbo-molecular pump. Additionally, a compound stage including a cylindrical member (not shown) extending from the exhaust end of the rotor 40 may be included to achieve a higher exhaust pressure and a higher inlet pressure.
Because of exacting temperature and cleanliness considerations in substrate processing, the substrate processing vacuum chambers are housed in an isolated clean room. Because the turbo molecular pumps must reduce pressure in the chambers down to 10xe2x88x927 Torr, they are necessarily located in the clean room adjacent the chambers to avoid any loss in pumping efficiency that would occur if the pumps were separated from the chambers by vacuum lines. Because the cost of building and maintaining clean rooms is so expensive, the physical size of components therein, including the turbo molecular pumps is always critical.
FIG. 2 is a simplified schematic, cross-sectional view of a vacuum substrate processing chamber 100 having a turbo-molecular pump 10 attached thereto. The turbo molecular pump 10 may be directly under the substrate 160 or offset, as depicted in FIG. 2. The chamber 100 and pump 10 make up part of a processing apparatus typically comprising several processing chambers and at least one transfer chamber. The substrate processing chamber 100 provides an isolated environment where the substrate 160 is processed through etching, deposition, implanting, cleaning, cooling and/or other pre-processing and post-processing steps. The substrate processing chamber 100 generally comprises an enclosure having side walls 104, a bottom 106 and a lid 108. A substrate support member 110 disposed in the bottom 106 of the chamber secures the substrate 160 in place during processing. The substrate support member 110 typically comprises a vacuum chuck or an electrostatic chuck to retain the substrate 160. A slit valve 112 is disposed on the chamber side wall 104 to allow the transfer of the substrate 160 into and out of the substrate processing chamber 100. In a CVD process, various process gases enter into the substrate processing chamber 100 through a gas inlet 120, such as a shower-head type gas inlet or nozzle, disposed through the lid 108 of the processing chamber. To exhaust the gases from the substrate processing chamber, a turbo-molecular pump 10 is attached to a gas outlet 130 of the substrate processing chamber 100.
Advances in substrate processing and increased capacity of vacuum processing chambers continuously call for higher capacity pumps. Some substrate processes like plasma-based etch and CVD processes require particularly high process gas flow rates and relatively shallow vacuum levels. As the flow rate of the reactants across the substrate processing surface is increased (i.e., the throughput of the vacuum pump increases to exhaust a higher volume), the time required for completion of the process is reduced. Thus, to increase throughput of the processing chamber, the vacuum pumping system used for plasma-based etch and CVD requires a high throughput or exhaust capacity. Furthermore, as the chamber sizes increase to accommodate larger substrates (i.e., 300 mm substrates), the turbo-molecular pumps used for these larger chambers must provide correspondingly larger exhaust capacities. For example, an exhaust capacity of 4000 l/sec. is required for a 300 mm chamber.
One way to decrease exhaust time and increase throughput of the pump is to increase the rotational speed of the rotor of the turbo-molecular pump. However, increasing the rotational speed of a rotor and the rotor blades necessarily results in additional stresses on the rotor and other components that can lead to failure of the pump components. Additionally, because of the high throughput of the process gases through the vacuum pump, unused reactants as well as reaction byproducts are removed from the processing chamber at a high rate and can either adhere to or react with the surfaces of the components inside the vacuum pump, causing the components to heat up significantly and resulting in breakdown of the component and the pump. For example, in HDP applications the pump internal components, such as a rotor, can rise to a temperature above 120xc2x0 C., and the stress caused by the high temperature can cause a physical break down of the component and the pump. Therefore, simply increasing the rotational speed of the pump is not a realistic solution.
Another way to increase the throughput or exhaust capacity of the vacuum pump and to decrease the time it takes to exhaust gases from a processing chamber is to increase the physical size of the turbo-molecular pump. For example, adding surface area to the blades of the rotor and stator by increasing their length will increase the flow of gas through the pump. However, because of the radial stresses brought to bear by the larger blades upon the rotor, the rotor must also be enlarged and strengthened to tolerate the larger blades. Likewise, the rotor bearings must be larger and more robust to compensate for the added vibration of the pump and there must be a corresponding increase in the size of the pump housing. The result is a pump with increased overall dimensions and weight. The larger pumps are more expensive to build, use additional energy to operate and cause more vibration in the clean room. Further, the larger pumps take up more of the precious envelope and clean room space below the vacuum chamber, giving the apparatus a larger footprint.
Therefore, there is a need for a turbo-molecular vacuum pump that provides a higher exhaust capacity than existing turbo-molecular pumps without a corresponding increase in the physical size and weight of the pump. There is a further need for a turbo molecular pump with enlarged capacity that requires a reduced amount of clean room space. There is a further need for a turbo molecular pump that creates less vibration than other pumps having the same capacity.
In one aspect, a vacuum processing system comprising a vacuum processing chamber and a turbo-molecular pump disposed on the vacuum processing chamber is provided. The turbo-molecular pump comprises a casing having an inlet port and an outlet port, a stator disposed on an inner wall of the casing, a rotor disposed in the stator, and a motor extending coaxially with the rotor, wherein at least the first stage of the pump is enlarged with no correspondingly larger pump components other than the corresponding upper portion of the housing.